Influence of Soil Properties on Stand Structure and Tree Species Diversity and Composition in the Upper Parana Atlantic Forest (Paraguay)

The Upper Parana Atlantic Forest harbors some of the most endangered ecosystems on the planet. Understanding the stand characteristics of these forests as well as their relationship with soil properties is vital to their conservation and restoration. The objective of this study was to clarify the relationship between soil properties and stand structure (individual density, basal area, and above ground biomass), tree species diversity (number of species and families, Simpson's and Shannon-Wiener Biodiversity Index), and tree species composition. We established 71 plots (50 × 20 m) distributed across eight protected areas in the Upper Parana Atlantic Forest managed by ITAIPU Binacional (Paraguay) and evaluated trees with DBH ≥ 10 cm and composite soil samples from 0 – 20 cm in depth. In all plots, we registered a total of 4,286 individuals corresponding to 218 morphotypes. We identified four forest types with their corresponding indicator species. Among these forest types, we observed significant differences between stand structure and tree species diversity. We separated the soil properties into two axes, with essential elements and pH on one axis and the balance of clay and sand contents on the other. We found statistically significant relationships between essential elements and pH with individual density and between the balance of clay and sand contents and tree species diversity. Both axes of soil properties were independently related with the forest types. The contents of essential elements and pH determined the difference between Forest Types I and II vs. Type III. On the other hand, the balance of clay and sand contents were linked to a difference in tree species diversity between Forest Types I and II. Forest Type IV is likely to be influenced strongly by nearby savanna rather than the two axes of soil properties. Our findings, i.e., two axes of soil properties and influence of nearby savanna, explain the heterogeneity of the tree community and contribute to our understanding of the Upper Parana Atlantic Forest, allowing more focused and informed forest restoration programs